U.S. soldiers inspect a suspected insurgent base in the Arab Jbur region of Iraq in June 2007. 19,429 enemy combatants have been killed since the '03 invasion. Militants are identified in the military database because they are linked to "hostile action," said Capt. Michael Greenberger, a Freedom of Information Act officer in Baghdad. There is no way to independently verify the data.

U.S. and Iraqi forces launched several large offensives aimed at crippling al-Qaeda since the arrival of more troops starting in February. The U.S. military says, however, there has been an increase in suicide attacks in recent days.

The size of the insurgency in Iraq has been difficult to measure and is fluid, making it hard to determine what impact the deaths have had on the insurgency in Iraq.

Last year, Gen. John Abizaid, then commander of military forces in the region, estimated the Sunni insurgency to be 10,000 to 20,000 fighters. He said the Shiite militia members were in the "low thousands." The U.S. military hasn't publicly provided any recent estimates.

There are 25,000 detainees in U.S. military custody in Iraq, according to the military. The numbers of enemy killed and detained would exceed the estimate given last year of the size of the insurgency.

Since the insurgency began after Baghdad fell in spring 2003, 19,429 militants have been killed in clashes with coalition forces, statistics show. The numbers do not include enemy killed during the invasion.

The statistics, provided at USA TODAY's request, were retrieved from a coalition database that tracks "significant acts." Militants are identified in the database because they are linked to "hostile action," said Capt. Michael Greenberger, a Freedom of Information Act officer in Baghdad. There is no way to independently verify the data.

"The information in the database is only as good as the information entered into it by operators on the ground at the time," Greenberger said. "Follow-up information to make corrections is done whenever possible."

The U.S. military rarely discusses the numbers of enemy dead, fearful of raising parallels with the Vietnam War when the U.S. military's reliance on "body counts" led to allegations of inflated figures because of political pressure to show results.

Today, U.S. commanders consider the number of enemy deaths a poor measure of progress in an insurgency and say there is no pressure to exaggerate. "The big difference is the command climate in Vietnam encouraged inflation," said T.X. Hammes, a retired Marine colonel and insurgency expert. "The general command climate (in Iraq) is: 'Don't exaggerate.' "

The military's new counterinsurgency manual emphasizes political and economic solutions to eliminate the conditions that breed militants. Those actions are considered more decisive than combat.

"You can't kill them all," Maj. Gen. Benjamin Mixon, commander of the American division responsible for northern Iraq, said in a recent interview.

The insurgency has been a mixture of Sunni groups, such as al-Qaeda, and Shiite militia extremists.

The enemy casualty numbers also reinforce the one-sided nature of battles on occasions when militants attempted to directly confront American forces.

The deadliest month for militants was August 2004 when thousands of militia fighters loyal to Shiite cleric Muqtada al-Sadr clashed with American forces in Najaf in southern Iraq. That month, 1,623 militants were killed. The U.S. military lost 53 troops in fighting during the same time.

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